The present invention relates to a method of processing seismic measurement-while-drilling (MWD) data and, more particularly, to a method of processing multi-component seismic measurement-while-drilling data.
Measurement-while-drilling involves the sensing of one or more downhole parameters during the drilling process. Sensors, typically mounted within drill collars located above the drill bit, are used to obtain information regarding the drilling process or subsurface conditions and a subset of these measurements may be transmitted to the surface, often using an acoustic or xe2x80x9cmud pulsexe2x80x9d telemetry system. Other measurements may be stored in recording devices located within the drill collars and this data can be retrieved when the drill bit is raised (also called xe2x80x9ctrippedxe2x80x9d) to the surface.
Seismic measurement-while-drilling data is acquired using seismic sensors, such as geophones or hydrophones that are typically located within a drill collar positioned above the drill bit. This type of equipment is described, for instance, in U.S. Pat. No. 5,585,556 and commonly assigned U.S. Pat. No. 6,308,137. In one multi-component embodiment of this type of equipment, three mutually orthogonal fixed axis geophones and a hydrophone are located in a drill collar. In this embodiment, one geophone may be oriented parallel to the longitudinal axis of the drill collar (referred to herein as the axially oriented geophone) and the other two geophones may be oriented perpendicular to each other in a plane that is perpendicular to this longitudinal axis (referred to herein as the first and second non-axially oriented geophones).
As the drill collar is not kept fixed by clamping during acquisition, it has been discovered that the drill collar can rotate around the axis of the well while multiple shots are being recorded at particular shot and receiver locations. One reason for making multiple recordings at a given combination of receiver and source location is to improve the signal-to-noise ratio of the data by stacking (i.e. by averaging or otherwise combining the data to attenuate random noise). When the drill collar has rotated during the acquisition of these multiple shots, it is clear that stacking the traces as they are acquired may not improve (and in fact may degrade) the quality of the data.
The use of software rotation techniques in the processing of multicomponent seismic data is known. See, for instance, xe2x80x9cAn Onshore Time-Lapse (4-D), Multicomponent, Data Processing Case History, Vacuum Field, New Mexicoxe2x80x9d, 1998 SEG Expanded Abstracts; xe2x80x9cFractured Reservoir Delineation Using Multicomponent Seismic Dataxe2x80x9d, Geophysical Prospective, 1997, 45,39-64; and the Colorado School of Mines, Reservoir Characterization Project, Phase VII Apr. 15-16, 1999 Sponsor Meeting Report (Chapter11) and Spring 2000. Report (Chapter 2)). While the use of these types of techniques is known, these techniques have not, heretofore, been used to align energy in multi-component seismic data along a common axis prior to a combining process such as stacking or to estimate the orientations and/or change in orientation of seismic sensors associated with two or more series of multi-component seismic MWD data acquired at different times at the same source and receiver locations.
Accordingly, it is an object of the present invention to provide an improved method of processing multi-component seismic measurement-while-drilling data.
One aspect of this invention involves a method of processing multi-component seismic measurement-while-drilling data that includes rotating the data to align energy in the data along a common axis and then combining the data. Another embodiment of the inventive method involves a technique for estimating the orientations and/or change in orientation of a bottom hole assembly associated with two or more series of multi-component seismic MWD data acquired at different times at the same source and receiver locations. Embodiments of the inventive method may be used to improve the signal to noise ratio of the data, to reduce downhole storage and transmission requirements, and to improve direct arrival time picks made using the data. Further features and applications of the present invention will be apparent from the figures and detailed description that follow.